This change contains a bunch of unit tests for the newly introduced
IndexDiffFilter. With these tests the code coverage of
IndexDiffFilter.include() is now 100%, i.e. every special case is
tested at least once.
Change-Id: Ib248d1cd16084f9c8e099006af151814c63c5941
Signed-off-by: Philipp Thun <philipp.thun@sap.com>